Juvenile periodontitis is a disease of teenagers and young adults characterized by rapid alveolar bone loss. An accumulation of microbiologic and immunologic evidence strongly suggests an association of the gram-negative rod, Actinobacillus actinomy-cetemcomitans with juvenile periodontitis. The exact role of this bacteria in the disease, if any, is not known. The objective of the work in this proposal is to make and begin to utilize monoclonal antibodies with specificity for Actinobacillus-antigens. Somatic cell hybridization techniques will be used to fuse antigen-sensitized Balb/c mouse splenic cells with the plasmacytoma, Sp2/0. Hybridomas synthesizing monoclonal antibodies directed against Actinobacillus will be detected and cloned. Monoclonal antibodies that identify antigens which are species-specific, strain-specific, and indicative of a group of A. actinomycetemcomitans isolates will be characterized. In addition, monoclonals against antigens on the Actinobacillus-associated leukotoxin will be made and utilized to examine the leukotoxin-host cell interactions. Well characterized monoclonals will be used to investigate the immunobiology of all available A. actinomycetemcomitans isolates and to examine the feasibility of using monoclonal antibodies to identify and localize A. actinomycetemcomitans-associated antigens on cells, in plaque, and in tissue. The information on the antigenic character of A. actinomycetemcomitans isolates and the monoclonal antibodies will prove to be of value in the microbiological and immunological approach to detection, treatment, and prevention of juvenile periodontitis.